The present invention relates to a safety device for controlling an ignition circuit for an internal combustion engine associated with a transmission coupling the engine to a load.
Internal combustion engines adapted to certain applications should not be started unless the transmission coupling the engine to a load is in neutral. For instance, if an engine for use as an outboard motor or an inboard motor is started with the transmission in gear, the boat begins to move immediately upon the start of the engine, with potential danger that the operator of the boat may fall into the water or the boat may run into another boat which may happen to be in the way of the first mentioned boat which has begun to move.
It has been suggested to provide a safety device to control the starting of the engine, so that the engine is not started unless the transmission is in neutral. This conventional safety device includes a thyristor adapted to be conductive to short the primary winding to prevent ignition. Before the engine is started, the thyristor is kept nonconductive provided that the transmission is in neutral. With the thyristor being nonconductive, ignition can be effected to start the engine. Once the engine is started, the transmission can be shifted into gear without rendering the thyristor conductive, by a function of a memory circuit, which includes a series circuit of a capacitor and a resistor to effectively memorize that the engine has been duly started so that it is no longer necessary to prevent ignition even if the transmission is in gear.
A disadvantage of the conventional safety device resides in that the series circuit of the capacitor and the resistor of the memory circuit is connected across the primary winding. When the thyristor is nonconductive and the ignition is effected, the series connection of the capacitor and the resistor across the primary winding prolongs the rise time of the secondary voltage of the ignition coil and decreases the magnitude of the secondary voltage.